U.S. patent number 5,315,645 [Application Number 07/624,983] was granted by the patent office on 1994-05-24 for communication apparatus utilizing digital optical signals.
This patent grant is currently assigned to Tek Electronics Manufacturing Corporation. Invention is credited to Mark Matheny.
United States Patent |
5,315,645 |
Matheny |
May 24, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Communication apparatus utilizing digital optical signals
Abstract
Communication apparatus using baseband, digitally formatted
optical signals provides an infrared optical communication link
between a terminal unit and station unit. Pulse width modulation or
continuously variable slope delta modulation digital procotols are
used to encode and decode the transmitted and received digital
optical signals. A microprocessor senses the presence of a
connection command signal to complete the optical communication
link. In one embodiment of the invention, a station unit associated
with a coin operated type pay telephone instrument communicates
with a remotely located terminal unit to permit a user to access
and be connected to the public telephone network via the terminal
unit. The station unit senses the digitally formatted optical
signal and decodes it to derive the supervisory and audio frequency
signals and in response to the supervisory signals causes the
telephone line to be connected to and disconnected from the station
unit. Electrical signals from the telephone line are digitally
encoded and transmitted via the optical communication link as
baseband digitally formatted optical signals to the terminal unit
where they are sensed, converted to electrical digital pulses,
decoded and transformed to an analog signal to excite a transducer
to produce an audible signal corresponding to the audio signal on
the telephone line.
Inventors: |
Matheny; Mark (Manchester,
CT) |
Assignee: |
Tek Electronics Manufacturing
Corporation (Manchester, CT)
|
Family
ID: |
24504116 |
Appl.
No.: |
07/624,983 |
Filed: |
December 10, 1990 |
Current U.S.
Class: |
379/144.01;
379/155; 379/56.1 |
Current CPC
Class: |
H04B
10/1143 (20130101); H04M 17/02 (20130101); H04M
1/737 (20130101) |
Current International
Class: |
H04B
10/10 (20060101); H04M 1/72 (20060101); H04M
1/737 (20060101); H04M 17/02 (20060101); H04M
17/00 (20060101); H04B 009/00 (); H04M
017/00 () |
Field of
Search: |
;379/144,56,58,61,155
;455/600,613,617,608 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chin; Stephen
Assistant Examiner: Loomis; Paul
Attorney, Agent or Firm: McCormick, Paulding & Huber
Claims
I claim:
1. Communication apparatus utilizing digital optical signals, said
apparatus comprising:
first input analog circuit means at a first location for receiving
an input analog electrical signal;
first digital circuit means coupled to said input analog circuit
means for converting said analog electrical signal to a digital
electrical signal;
first optical transmission circuit means coupled to said first
digital circuit means for generating and transmitting a first
baseband digitally formatted optical signal;
enabling circuit means coupled to said first optical transmission
circuit means for enabling said first optical transmission circuit
means to transmit a connection command signal;
first optical receiving circuit means located remotely from and in
line-of-sight alignment with said first optical transmission
circuit means for sensing and receiving said baseband digitally
formatted optical signal and for converting said baseband digital
formatted optical signal to a digital electrical signal, and
second digital circuit means coupled to said first optical
receiving circuit means for converting said digital electrical
signal to an output analog electrical signal, said output analog
electrical signal replicating said input analog electrical
signal;
said first digital circuit means further comprising a continuously
variable slope delta modulation circuit and said second digital
circuit means further comprising a continuously variable slope
delta demodulation circuit.
2. Communication apparatus utilizing digital optical signals, said
apparatus comprising:
first input analog circuit means at a first location for receiving
an input analog electrical signal;
first digital circuit means coupled to said input circuit means for
converting said analog electrical signal to a digital electrical
signal;
first optical transmission circuit means coupled to said first
digital circuit means for generating and transmitting a first
baseband digitally formatted optical signal;
enabling circuit means coupled to said first optical transmission
circuit means for enabling said first optical transmission circuit
means to transmit a connection command signal;
first optical receiving circuit means located remotely from and in
line-of-sight alignment with said first optical transmission
circuit means for sensing and receiving said baseband digitally
formatted optical signal and for converting said baseband digital
formatted optical signal to a digital electrical signal, and
second digital circuit means coupled to said first optical
receiving circuit means for converting said digital electrical
signal to an output analog electrical signal, said output analog
electrical signal replicating said input analog electrical
signal;
said first digital circuit means further comprising a
pulse-width-modulation modulator and said second digital circuit
means further comprising a pulse-width-modulation demodulator.
3. Communication apparatus as defined in claims 1 or 2 further
including:
second input circuit means for receiving a second input analog
electric signal;
third digital circuit means coupled to said second input circuit
means for converting said second input analog electrical signal to
an encoded digital electrical signal, said third digital circuit
means having an output coupled to said second optical transmission
circuit means, said second optical transmission circuit means being
responsive to said digital electrical signal to transmit a second
baseband digitally formatted optical signal representative of said
encoded digital electrical signal, and
fourth digital circuit means coupled to said second optical
receiving circuit means for decoding said encoded digital
electrical signal and for converting said digital electrical signal
to an analog electrical signal.
4. Communication apparatus as defined in claim 3 further
including:
signalling circuit means coupled to said first input circuit means
for generating one or more unique control signals for use by said
microprocessor to control said communication apparatus, and
control signal circuit recognition means coupled to said second
digital circuit means and to said microprocessor circuit means for
sensing said one or more unique control signals, said
microprocessor producing an output control command signal in
response to and corresponding to said unique control signal
generated at said signalling circuit means.
5. Communication apparatus as defined in claim 4 wherein said
signalling circuit means comprises a dual tone multi-frequency
(DTMF) generator and said control signal circuit recognition means
comprises a DTMF receiver and decoder.
6. Communication apparatus as defined in claim 3 wherein said first
and second baseband digitally formatted optical signals are
infrared optical signals.
7. Communication apparatus utilizing digital optical signals, said
apparatus comprising:
first input circuit means for receiving an input analog electrical
signal;
first digital circuit means coupled to said input circuit means for
converting said analog electrical signal to a digital electrical
signal;
first optical transmission circuit means coupled to said first
digital circuit means for generating and transmitting a first
baseband digitally formatted optical signal;
first optical receiving circuit means located remotely from and in
line-of-sight alignment with said first optical transmission
circuit means for sensing and receiving said baseband digitally
formatted optical signal and for converting said baseband digital
formatted optical signal to a digital electrical signal,
second digital circuit means coupled to said first optical
receiving circuit means for converting said digital electrical
signal to an output analog electrical signal, said output analog
electrical signal replicating said input analog electrical
signal;
enabling circuit means coupled to said first optical transmission
circuit means for enabling said first optical transmission circuit
means to transmit a connection command signal;
microprocessor circuit means coupled to said first optical
receiving circuit means for sensing and responding to said
connection command signal to generate an enable command signal;
second optical transmission circuit means coupled to said
microprocessor circuit means for receiving said enable command
signal in response to said microprocessor sensing said connection
command signal to enable said second optical transmission circuit
means to transmit a digitally formatted optical signal
acknowledging said connection command signal, and
second optical receiving circuit means located in the vicinity of
said first optical transmission circuit means and remotely from and
in line-of-sight alignment with said second optical transmission
circuit for receiving said digitally formatted optical signal
carrying said acknowledgement response signal to said connection
command signal whereby a two-way optical communication link between
said first optical transmission circuit means and said first
optical receiving circuit means and between said second optical
transmission circuit means and said second optical receiving
circuit means is established.
8. Communication apparatus as defined in claim 7 further including
target lock signalling means coupled to said microprocessor circuit
means for providing an indication that said optical communication
link is established and that said first optical transmission
circuit means is in line-of-sight alignment with said first optical
receiving circuit means.
9. Communication apparatus utilizing infrared digital optical
signals for establishing a bidirectional optical communication path
between a first and second location remote from one another, said
apparatus comprising:
a terminal unit at the first location, said terminal unit
including:
means for receiving a first analog electrical signal;
means coupled to said first analog receiving means for converting
said first analog electrical signal to a first baseband digitally
formatted optical signal;
first means for transmitting said first baseband digitally
formatted optical signal;
first means for enabling said first transmitting means to transmit
a first connection command signal;
a station unit at the second location, said station unit
including:
means for receiving said first baseband digitally formatted optical
signal;
means coupled to said first optical receiving means for converting
said received first baseband digitally formatted optical signal
into a second analog electrical signal, said second analog
electrical signal replicating said first analog electrical
signal;
means for receiving a third analog electrical signal;
means coupled to said third analog receiving means for converting
said third analog electrical signal to a second baseband digitally
formatted optical signal;
second means for transmitting said second baseband digitally
formatted optical signal;
second means for enabling said second transmitting means to
transmit a second connection command signal;
said terminal unit further including:
means for receiving said second baseband digitally formatted
optical signal;
means coupled to said second optical receiving means for converting
said received second baseband digitally formatted optical signal
into a fourth analog electrical signal, said fourth analog
electrical signal replicating said third analog electrical signal
to establish a two-way communication connection between the first
and second locations via the bi-directional optical communication
path.
10. Communication apparatus utilizing infrared digital optical
signals as defined in claim 9 wherein said means for converting
said first analog electrical signal and said means for converting
said third analog electrical signal comprise a digital modulator,
and said means for converting said received first baseband
digitally formatted optical signal and said means for converting
said received second baseband digitally formatted optical signal
comprise a digital demodulator.
11. Communication apparatus utilizing infrared digital optical
signals as defined in claim 10 wherein said digital modulator and
said digital demodulator comprise a continuously variable slope
delta (CVSD) modulator and demodulator, respectively.
12. Communication apparatus utilizing infrared digital optical
signals as defined in claim 10 wherein said digital modulator and
said digital demodulator comprise a pulse width modulation (PWM)
modulator and demodulator, respectively.
13. Communication apparatus utilizing infrared digital optical
signals as defined in claim 10 further including:
said means for converting said first baseband digitally formatted
optical signal comprising:
a first photo detector for converting said infrared digital optical
signals to corresponding digital electrical signals;
at least one stage of first amplification circuit means coupled to
said photo detector for amplifying said corresponding digital
electrical signals;
first switchable amplification circuit means having an input
coupled to said at least one stage of amplification circuit
means;
first switching circuit means coupled to said first switchable
amplification circuit means and having two operative states, said
first operative state for bypassing said first switchable
amplification circuit means and corresponding to said apparatus
operating at a SHORT distance between said first and second
locations and said second operative state for coupling said first
switchable amplification circuit means to said digital demodulator
and corresponding to said apparatus operating at a LONG distance
between said first and second locations;
said means for converting said second baseband digitally formatted
optical signal comprising:
a second photo detector for converting said infrared digital
optical signals to corresponding digital electrical signals;
at least one stage of second amplification circuit means coupled to
said second photo detector for amplifying said corresponding
digital electrical signals;
second switchable amplification circuit means having an input
coupled to said at least one stage of second amplification circuit
means;
second switching circuit means coupled to said second switchable
amplification circuit means and having two operative states, said
first operative state for bypassing said second switchable
amplification circuit means and corresponding to said apparatus
operating at said SHORT distance and said second operative state
for coupling said second switchable amplification circuit means to
said second digital demodulator and corresponding to said apparatus
operating at said LONG distance between said first and second
locations.
14. Communication apparatus utilizing infrared digital optical
signals as defined in claim 13 further including:
said means for transmitting said first baseband digitally formatted
optical signal comprising first LED circuit means, and
said means for transmitting said second baseband digitally
formatted optical signal comprising second LED circuit means.
15. Communication apparatus utilizing infrared digital optical
signals as defined in claim 14 further including said digitally
formatted optical signal being transmitted at a predetermined
frequency, said predetermined frequency corresponding to a
connection command signal, said communication command signal being
sensed by said means for converting said first baseband digitally
formatted optical signal to maintain said optical communication
path.
16. Communication apparatus utilizing infrared digital optical
signals as defined in claim 15 further comprising said means for
converting said first baseband digitally formatted optical signal
including logic circuit means for sensing said communication
command signal.
17. Communication apparatus utilizing infrared digital optical
signals as defined in claim 16 wherein said logic circuit means
comprises a microprocessor having an instruction set for sensing
and detecting said communication command signal to enable said
second LED circuit means.
18. In combination with a telephone instrument of the general type
arranged to accept coin, credit card and the like for accessing
connection to the public telephone switching network, apparatus for
establishing a bi-directional optical communication path between a
user and the telephone switching network, said apparatus
comprising:
a station unit;
a terminal unit located remotely from said station unit;
said station unit having circuit means for electrically interfacing
a telephone line associated with the public telephone switching
network and the telephone instrument to electrically and physically
couple the telephone line to the telephone instrument, said station
unit having first and second operative states, said first state
corresponding to the telephone line being electrically connected to
the telephone instrument in the normal manner and said second state
corresponding to the telephone line being electrically connected
said station unit circuit means;
said terminal unit having means for optically coupling said
terminal unit to said station unit, said terminal unit further
comprising:
microphone means for sensing audio frequency signals and for
converting said audio signals to baseband frequency electrical
signals, said microphone means having an output;
receiver earpiece means for sensing baseband frequency electrical
signals carrying information in the audio frequency spectrum to
convert said sensed electrical signals to sound for hearing by a
user;
a key pad having circuit means for generating dual tone
multi-frequency (DTMF) signals at an output to dial a telephone
number;
supervisory circuit means for generating a baseband frequency
supervisory signal representative of an "off-hook" condition for
initiating a call connection with said station unit, said
supervisory signal being used for sustaining said optical coupling
between said station unit and said terminal unit;
digital modulation circuit means for converting said baseband
frequency supervisory signals and said baseband frequency audio
signals to digitally modulated electrical signals;
optical circuit means coupled to said digital modulation circuit
means for converting said digitally modulated electrical signals
into digitally modulated optical signals for transmission to said
station unit;
optical receiving means for sensing optical signals and for
converting said sensed optical signals into digitally modulated
electrical signals representative of supervisory and audio
frequency signals originating at said station unit;
first digital demodulation circuit means for converting said
digitally modulated electrical signals into supervisory and audio
baseband frequency signals;
said station unit means including:
optical detecting means for receiving a digitally modulated optical
signal from said terminal unit to transform said optical signal to
a corresponding digitally modulated electrical signal;
second digital demodulation circuit means for converting said
digitally modulated electrical signal into supervisory and audio
baseband frequency signals;
circuit means response to an "off-hook" supervisory signal for
causing said station unit to operate to its second operative state
and for coupling baseband frequency electrical signals appearing on
the telephone line to said second digital modulation circuit means
for converting said baseband frequency signals to digitally
modulated electrical signals;
optical transmission circuit means for converting said digitally
modulated electrical signals to digitally modulated optical signals
for transmission to said terminal unit, whereby audio frequency
signals appearing on said telephone line are received at the
earpiece of said terminal unit and audio frequency signals at the
microphone of said terminal unit are received at said telephone
line.
19. Apparatus as defined in claim 18 wherein said digital
modulation circuit means and said digital demodulation circuit
means process pulse-width-modulated (PWM) electrical signals.
20. Apparatus as defined in claim 19 wherein said digital
modulation circuit means and said digital demodulation circuit
means process continuous variable slope delta (CVSD) modulated
electrical signals.
21. Communication apparatus utilizing digital optical signals, said
apparatus comprising:
first input circuit means for receiving an input analog electrical
signal;
first digital circuit means coupled to said input circuit means for
converting said analog electrical signal to a digital electrical
signal;
first optical transmission circuit means coupled to said first
digital circuit means for generating and transmitting a first
baseband digitally formatted optical signal;
enabling circuit means coupled to said first optical transmission
circuit means for enabling said first optical transmission circuit
means to transmit a connection command signal;
first optical receiving circuit means located remotely from and in
line-of-sight alignment with said first optical transmission
circuit means for sensing and receiving said baseband digitally
formatted optical signal and for converting said baseband digital
formatted optical signal to a digital electrical signal, and
second digital circuit means coupled to said first optical
receiving circuit means for converting said digital electrical
signal to an output analog electrical signal, said output analog
electrical signal replicating said input analog electrical
signal.
22. A communication method utilizing digital optical signals, said
method comprising the steps of:
receiving a first analog electrical signal at a first location;
converting said first analog electrical signal to a first baseband
digitally formatted optical signal;
transmitting said first baseband digitally formatted optical
signal;
receiving said first baseband digitally formatted optical signal at
a second location remote from said first location,
converting said received first baseband digitally formatted optical
signal into a second analog electrical signal, said second analog
electrical signal replicating said first analog electrical
signal;
the step of converting said first analog electrical signal further
including processing said first analog electrical signal utilizing
a continuously variable slope delta (CVSD) modulation encoder and
digitally encoding said first analog electrical signal at a
predetermined frequency, and
the step of receiving said first baseband digitally formatted
optical signal including sensing said transmitted first baseband
digitally formatted signal at said predetermined frequency thereby
establishing an optical communication link between the first and
second location when said digitally formatted signal is sensed at
said predetermined frequency at the second location and dropping
said optical communication link when said digitally formatted
signal is not sensed at said predetermined frequency at the second
location.
23. A communication method utilizing digital optical signals, said
method comprising the steps of:
receiving a first analog electrical signal at a first location;
converting said first analog electrical signal to a first baseband
digitally formatted optical signal;
transmitting said first baseband digitally formatted optical
signal;
receiving said first baseband digitally formatted optical signal at
a second location remote from said first location, and
converting said received first baseband digitally formatted optical
signal into a second analog electrical signal, said second analog
electrical signal replicating said first analog electrical
signal;
the step of converting said first analog electrical signal further
including processing said first analog electrical signal utilizing
a pulse-width-modulation (PWM) encoder and digitally encoding said
first analog electrical signal at a predetermined frequency,
and
the step of receiving said first baseband digitally formatted
optical signal including sensing said transmitted first baseband
digitally formatted signal at said predetermined frequency thereby
establishing an optical communication link between the first and
second location when said digitally formatted signal is sensed at
said predetermined frequency at the second location and dropping
said optical communication link when said digitally formatted
signal is not sensed at said predetermined frequency at the second
location.
24. A communication method as defined in claim 22 wherein the step
of converting said received first baseband digitally formatted
optical signal includes processing said received optical signal
utilizing a continuously variable slope delta (CVSD) modulation
decoder.
25. A communication method as defined in claim 23 wherein the step
of converting said received first baseband digitally formatted
optical signal includes processing said received optical signal
utilizing a pulse-width-modulation (PWM) decoder.
26. A communication method as defined in claim 22 or 23 further
including the steps of:
receiving a third analog electrical signal at the second
location;
converting said third analog electrical signal to a second baseband
digitally formatted optical signal;
transmitting said second baseband digitally formatted optical
signal;
receiving said second baseband digitally formatted optical signal
at the said first location, and
converting said received second baseband digitally formatted signal
into a fourth analog electrical signal, said fourth analog
electrical signal replicating said third analog electrical signal
to establish a bi-directional digital optical communication link
between the first and second locations.
27. A communication method as defined in claim 26 wherein the steps
of converting said first and second analog electrical signals to
first and second baseband digitally formatted optical signals,
respectively include the step of converting said first and second
analog electrically signals to digitally formatted infrared optical
signals.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to optically coupled
communication apparatus comprising a terminal unit and station unit
located remotely from one another and deals more particularly with
communication apparatus utlizing baseband digitally formatted
optical signals to establish a two-way optical communication link
between a terminal unit and a station unit. The invention also
deals specifically with communication on the public telephone
network wherein a user via a remote, portable, terminal unit
establishes a two-way digitally formatted optical communication
link with a coin operated pay telephone instrument and the like
equipped with the station unit of the invention.
Telephonic communications via the public telephone network has
grown substantially over the past few years as the numbers of the
traveling public become larger and as more and more people become
reliant on the ability to communicate with others to gain their
livelihood, such as, for example, salesmen and the like. Such
communication is generally accomplished utilizing the so called pay
or coin operated telephone instrument and includes credit card and
the like type operated telephone instruments. In order to meet the
increased demand for access to the public telephone network, the so
called cellular type telephone service was introduced wherein a
user is assigned a dedicated telephone number and may originate and
receive telephone calls by means of a cellular type telephone
instrument cooperating with a mobile radio receiver. Although
cellular type telephone service permits a user to place and receive
a call from any location within a cellular area from his own
cellular telephone, cellular telephone instruments and cellular
telephone service are relatively expensive and in some instances
not available in all geographic locations. Accordingly, the
majority of telephone callers still access the public telephone
network via conventional coin operated, credit card and the like
type telephone instruments.
Applicant's U.S. Pat. No. 4,829,561, assigned to the same assignee
as the present invention and incorporated herein by reference,
discloses apparatus for optically coupling a terminal unit to the
public telephone network through a pay telephone instrument and the
like wherein the optical communication link is established by the
"brute force" transmission of baseband audio frequency signals that
have been converted to an energy beam typically an infra-red
optical signal. The device of the above-referenced patent utilizes
baseband analog techniques and is susceptible to the limitations
and problems generally associated with any device utilizing analog
baseband frequency operation.
The aim therefore of the present invention is to provide
communication apparatus utilizing a digital communications protocol
to generate a digitally formatted optical signal to provide a
two-way communication link between a terminal unit and a station
unit located remotely from and in line-of-sight alignment with one
another.
It is a further object of the present invention to provide a
telephonic device that is portable and personal to a user and which
permits access to the public telephone network while overcoming
disadvantages associated with conventional coin-operated operated,
credit card and the like type telephone instruments.
SUMMARY OF THE INVENTION
In accordance with the present invention, communication apparatus
and a related method utilizing digital optical signals for
establishing a bi-directional optical communication path between a
first and second location remote from one another is presented. An
analog signal representative of for example, voice, is converted by
a digital modulator to a digital electrical signal to drive an
optical transmission circuit to generate and transmit a baseband
digitally formatted optical signal. An optical receiving circuit is
located remotely from the optical transmission circuit and in
line-of-sight alignment to sense and receive the baseband digitally
formatted signal. The received digitally formatted optical signal
is converted by a digital demodulator to an analog electrical
signal replicating the input analog electrical signal.
The invention further comprises a second circuit for receiving an
input analog electrical signal which is processed by a digital
modulator to a digital electrical signal to drive an optical
transmission circuit which generates and transmits a second
baseband digitally formatted optical signal. The second baseband
digitally formatted optical signal is sent to the first location to
complete a bi-directional optical communication path preferably
utilizing infrared optical signals. The received second baseband
digitally formatted optical signal is processed by a digital
demodulator to generate a fourth analog signal replicating the
third analog input signal.
In a further embodiment of the invention, apparatus for
establishing a bi-directional optical communication path between a
user and a telephone switching network is presented in combination
with a telephone instrument of the general type arranged with coin,
credit card and the like for accessing connection to the public
telephone switching network. A station unit electrically interfaces
a telephone line associated with the public telephone switching
network and the telephone instrument and has two operative states
corresponding to the telephone line being electrically connected to
the telephone instrument in the normal manner and corresponding to
the telephone line being electrically connected to the station
unit, respectively. A terminal unit is located remotely from the
station unit and transmits digitally formatted optical signals
representative of voice or other audio signals present at the
terminal unit in audible form which are transformed by a microphone
into an analog electrical signal. The analog signal and supervisory
signals which are generated from a keypad utilizing dual tone
multifrequency (DTMF) signals representative of supervisory signals
and telephone number digits are processed by a digital modulator
and converted to digital electrical signals which drive LED's or
other optical devices to generate the digitally formatted optical
signals which are transmitted to the station unit. An optical
receiver at the station unit senses the transmitted optical signals
and converts them to digital electrical signals which are processed
by a digital decoder into analog electrical signals. The analog
signals are coupled to the telephone line and replicate the
electrical signal representative of the audible input at the
terminal unit.
A further aspect of the invention utilizes a microprocessor circuit
to sense the presence of a digital electrical signal having a
predetermined frequency to initiate a connection with the terminal
unit. The microprocessor then enables an optical transmitter at the
station unit to transmit a digitally formatted optical signal to
the terminal unit to establish the bi-directional optical
communication path over which electrical analog signals present at
the telephone line are transmitted a digitally formatted optical
signals to the terminal unit. The digital optical signals are
sensed and decoded by a digital demodulator, converted to an analog
electrical signal and transformed via an earpiece to an audible
signal heard by the user.
In a further aspect of the invention, a voice synthesis message
circuit is controlled by the microprocessor and provides
instructional messages, advertisements and the like to the user
during the calling sequence.
In a yet further aspect of the invention, the microprocessor
maintains the connection to the telephone line for a predetermined
time during which the optical communication link between the
terminal unit and station unit is broken or interrupted before
dropping the connection to the telephone line. This feature
compensates for momentary interruptions of the continuous
transmission of digitally formatted optical signals at the
predetermined frequency due to people breaking the optical
communication link by walking through or by other objects
interfering with the path which prevents the terminal unit and
station unit to be in line-of-sight alignment.
BRIEF DESCRIPTION OF THE DRAWINGS
Additional objects, features and advantages of the present
invention will become readily apparent from the following written
description and claims taken in conjunction with the drawings
wherein:
FIG. 1 is a perspective, somewhat conceptual illustration showing
the transmitter portion of the terminal unit of the invention
attached to an automobile visor and aimed in the vicinity of the
station unit of the invention arranged to cooperate with a pay
telephone.
FIG. 2 is a somewhat perspective, exploded view of the station unit
embodying the present invention showing one possible mounting
arrangement with the pay telephone.
FIG. 3 is a somewhat perspective view of the terminal unit
embodying the present invention wherein the digitally formatted
optical signal receiver/transmitter unit is separate from the
handset containing the earpiece, microphone and keypad.
FIG. 4 is a schematic block diagram showing the major functional
components of the terminal unit of the present invention.
FIG. 5 is a schematic block diagram showing the major functional
components of the station unit embodying the present invention.
FIG. 6 is an electrical schematic and function block circuit
diagram showing one possible implementation of the terminal unit of
the present invention.
FIG. 7 is an electrical schematic and function block diagram
showing one possible implementation the station unit of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Prior to describing several preferred embodiments, it will be
recognized that the present invention may be utilized in any
environment to provide a communication link between two remote
locations wherein a digitally formatted optical signal is
transmitted at baseband to carry information over the optical
communication link between the two locations. Transmission of the
digitally formatted optical signal at baseband means the
transmission is made without using a carrier signal and further
there is only one transmission channel. Such a two way optical
communication link might be, for example, between two buildings,
between two locations within the interior of a building, between
remote locations outdoors, or between any two remote locations
wherein a line-of-sight alignment is possible. Several preferred
embodiments are described hereinbelow by way of example rather than
limitation.
Turning now to the drawings and considering FIGS. 1 and 2, the
present invention is disclosed in one embodiment in combination
with a telephone instrument of the general type arranged to accept
coin, credit card, and the like for accessing a connection to the
public telephone switching network.
FIG. 1 illustrates the receiver/transmitter unit portion 10 of a
terminal unit 11 embodying the present invention wherein the
receiver/transmitter unit 10 is mounted on a visor 12 of an
automobile and oriented such that the receiver/transmitter unit 10
is aimed generally in the direction of a station unit which
receives the digitally formatted optical signals and interfaces
with a coin operated pay type telephone instrument as best viewed
in FIG. 2.
In FIG. 2, the coin operated pay type telephone instrument is
designated 14 and is mounted in a typical telephone enclosure unit
generally designated 16. The station unit portion is generally
designated 18 and is shown in a slightly exploded view. The station
unit 18, in one embodiment, includes a base 20 and cover 22 which
provide means for mounting and enclosing an electronic circuit
board 24 upon which circuit board are mounted electronic
components, relays, connectors, integrated circuits, etc. generally
designated for illustrative purposes 26,26 and which comprise the
electronic circuitry of the station unit.
The circuit board 24 also includes one or more optical devices such
as, light emitting diodes (LED) 28 for generating an energy beam,
for example, an optical beam 30. The station unit 18 also includes
at least one optical sensing and detecting device such as a photo
diode 32 for receiving an energy beam, for example, an optical beam
34 originating at and being transmitted from the
receiver/transmitter unit 10. Typically, the station unit 18 may
also include optical filters 36 and 38 through which the optical
beams 30 and 34, respectively, pass. The optical filter serves to
limit the energy sensed by the photo diode and which energy is in
the form of visible or ambient light which may tend to degrade the
optical signal transmitted and received between the terminal unit
and station unit.
The circuit board 24 includes a visual indicator or lamp 40 which
functions as a target and illuminates to alert a user that the
receiver/transmitter unit 10 is aimed and oriented correctly to
establish and maintain the two way optical communication link
between the receiver/transmitter unit 10 and the station unit 18.
The target lamp 40 is illustrated in FIG. 2 in alignment with an
opening 42 in the base 20 and through which opening the visual
target indicating light beam 44 may be seen by the user.
Turning now to FIG. 3, one embodiment of the terminal unit 11 is
shown wherein the terminal unit 11 includes a handset generally
designated 46, a receiver/transmitter unit generally designated 10,
and a power plug generally designated 48. The handset 46 comprises
a keypad generally designated 50, a microphone built into the
handset and generally designated 52, and an earphone generally
designated 54 also built into the handset. The power required for
the electronic circuitry within the handset 46 and the
receiver/transmitter unit 10 is supplied from a power plug 48
adapted to be inserted into the cigarette lighter receptacle in the
case of a terminal unit designed for use with a vehicle. Typically,
a battery voltage potential from the battery of the vehicle is
applied at the tip 56 and ground reference potential is applied to
the side terminals 58,58 of the power plug 48. Both the battery
voltage potential and the ground reference potential are connected
to corresponding electrical wires within an electrical conduit 60
and which wires carry the voltage and ground reference potentials
from the power plug 48 to the handset 10. The handset 10 is in turn
connected via wires within an electrical conductor or sheath 62 to
the receiver/transmitter unit 10. It will be recognized by those
skilled in the art that power for the handset 46 and
receiver/transmitter unit 10 may be supplied by well known power
source means other than the vehicle battery.
The receiver/transmitter unit 10 includes, in the illustrated
embodiment, a visor clip 64 for attaching the receiver/transmitter
10 to the visor of a vehicle as illustrated in FIG. 1. The
receiver/transmitter unit 10 also generates, as illustrated
schematically in FIGS. 1 and 4, optical beam 34 produced by one or
more light emitting diodes (LED) located behind an optical filter
33. The receiver/transmitter unit 10 also includes optical detector
devices located behind an optical filter 35 for sensing and
detecting an optical beam 30 produced by the station unit located
remotely from the terminal unit and which station unit is not
illustrated in FIG. 3. It will be understood that the handset 46
and the receiver/transmitter unit 10 may be packaged as a single
integral unit and may also include an internally housed battery.
For example, the terminal unit 11 may be packaged to be fit into a
user's briefcase and to operate with a station unit at a pay
telephone instrument located in an airport, railroad station, or
other such area where pay telephone instruments are generally
located.
As explained and described in further detail below, an initiate
communication link or connection command is generated at the
handset by operating a switch generally designated 66 from an OFF
position to an ON position to activate the electronic circuitry
generating the initiate communication link or connection command
signal which is transmitted to the station unit via the optical
beam. The handset may also include an indicator, such as an LED 68,
to alert the user that the terminal unit 11 has been activated to
generate the initiate communication link or connection command
signal.
Turning now to FIGS. 4 and 5, FIG. 4 illustrates in block diagram
form the major functional component blocks of the terminal unit 11
and FIG. 5 illustrates in block diagram form the major functional
component blocks of the station unit 18 embodying the present
invention. Still referring to FIGS. 4 and 5, an optical
communication link between the terminal unit and station unit
utilizing the digitally formatted optical wave to provide the
communication between the terminal unit 11 and the station unit 18
is established as follows. A user generates a request for service
by first turning on the handset by operating the ON/OFF switch
represented by the ON/OFF enable function block 72 to the ON
position to enable the LED driver circuit means designated by the
functional block 70 which is coupled to the ON/OFF enable function
block 72 via the lead 74. The ON/OFF enable function block 72 is
also coupled to the output 76 of a digital modulator circuit means
designated by the function block 78 via a lead 80 to enable and
disable the output 76. On enablement, the digital modulator circuit
means 78 generates the initiate communication link or connection
command signal as a 56 kilohertz square wave signal to initiate and
maintain the communication link. The 56 kilohertz wave signal is
coupled through the buffer amplifier circuit means designated by
the function block 82 which has its output 84 coupled to the input
of the LED circuit driver means 70. The output 86 of the LED driver
circuit means 70 is coupled to one or more light emitting diodes
designated by the function block 88 to switch the LEDs on and off
at the 56 kilohertz rate to generate the digitally formatted
optical wave 34.
The digitally formatted optical wave 34 passes through the optical
filter 38 at the station unit 18 and is sensed and detected by a
photo diode 90 or other suitable device for receiving and detecting
the optical wave being transmitted. The output 92 of the detector
90 is coupled to amplification and rejection electronic circuitry
represented generally by the function block 94 to remove AC noise
from the received signal and to amplify the signal. The signal is
also conditioned to provide digital pulses having sharp leading and
trailing edges. The output 96 of the amplification and conditioning
circuitry shown in function block 94 is coupled to an input 98 of a
microprocessor shown generally in function block 100.
The microprocessor 100 includes an instruction set which senses the
frequency of the incoming signal by measuring the time between
successive transitions in the signal to determine if the signal is
the 56 kilohertz connection command signal. Upon detection of the
connection command signal, the microprocessor generates an enable
signal at its output 102 which is coupled to an input 104 of an LED
driver circuit means shown generally within the function block 106.
The microprocessor 100 also has an output 108 connected to an
illumination device shown within the function block 110 and which
illumination device serves as the "target lock" indication to the
user that the alignment between the terminal unit and the station
unit is proper and that the connection command signal has been
received and detected to complete the handshake sequence. The
illumination of the "target lock" indication makes the user aware
that the communication link has been established between the
terminal unit and the station unit and serves as a prompt to the
user to now go "OFF-HOOK". The microprocessor is used to facilitate
the circuit operation and provide flexibility and ease to adjust
timing and detection parameters; however, the microprocessor basic
functions can be duplicated using logic circuit implementation.
Still referring to FIGS. 4 and 5, the user generates an OFF-HOOK
supervisory signal by depressing a predetermined key on the keypad
generally shown within the function block 112, to generate a dual
tone multi-frequency (DTMF) analog signal at its output 114 which
is coupled to the input of an amplifier shown within the function
block 116. The DTMF signal is coupled from the output 118 of the
amplifier 116 to the digital modulator circuit means 78. The DTMF
signal appearing at the input to the digital modulator is converted
to a series of digital pulses utilizing pulse width modulation
(PWM) or continuously variable slope delta (CVSD) modulation
encoding techniques. The analog DTMF signal at the input to the
digital modulator circuit 78 now appears at the output 76 as a
train of digital pulses which are coupled to the LED driver circuit
means through the buffer amplifier circuit 82 to drive at least one
LED 88 biasing it ON and OFF to cause it to emit a digitally
formatted optical wave corresponding to the series of digital
pulses at the output 76 of the digital modulator. The digitally
formatted optical wave contains encoded in digital format, the
analog information representative of the OFF-HOOK DTMF supervisory
signal generated.
As in the case of the connection command signal, the digitally
formatted optical wave signal is received and detected by the photo
diode 90 and amplified and conditioned by the amplification and
conditioning circuitry in the function block 94. The output of the
amplification and conditioning circuit 96 is coupled to the input
of a digital demodulator circuit means generally contained within
the function block designated 120. The type of digital demodulator
circuit corresponds to the digital modulator circuit utilized in
the digital communication protocol being used. That is, the
demodulator will be a pulse width demodulator if a pulse width
modulator is used, and likewise will be a continuously variable
slope delta demodulator if a continuously variable slope delta
modulator is used. The digital demodulator circuit 120 processes
the digital pulse train input representative of the analog DTMF
supervisory signal transmitted and provides an analog replication
of the DTMF signal at its output 122. The DTMF signal is coupled to
a DTMF detector and latching circuit means illustrated generally by
the function block 124 which in turn provides an address signal on
lead 126 which is coupled to the microprocessor 100. The
instruction set within the microprocessor 100 detects and
determines that the signal received is an OFF-HOOK supervisory
signal and responds by providing a communication connect command
signal on lead 128 which is coupled to the DTMF detector and
latching circuit means shown within the function block 124. The
output 130 of the DTMF detector and latching circuit 124 in the
illustrated embodiment operates a relay 132 which provides
connections to the pay telephone instrument 134 and the tip and
ring of the telephone line shown as lead 136 and to a two
wire-to-four wire hybrid converter circuit 138 via leads 140. The
hybrid converter 138 is connected to a transmit isolator circuit
142 via leads 144 and also to a receive isolator circuit 146 via
leads 148. The operation of the receive isolator, transmit
isolator, hybrid converter, telephone instrument and respective
interconnection with the telephone line are well known to those
skilled in the art and are shown for exemplary and illustrative
purposes within the dashed line box 150. It will also be recognized
by those skilled in the art that the dashed line box 150 may be any
communication device which transmits and/or receives electrical
signals.
Still considering FIGS. 4 and 5, the phone line 136 is coupled upon
operation of the relay 132 through the hybrid circuit to the
transmit isolator and returns dial tone in the form of an analog
electrical signal which is coupled to the input 152 of a buffer
amplifier circuit means shown within the function block 154. The
output of the amplifier 154 is coupled to the input 156 of a
digital modulator circuit means shown within the function block
158. The digital modulator circuit transforms the analog electrical
signal at the input 156 to a series of digital pulses at its output
160 which are coupled to the LED driver circuit means 106. The
output 162 of the LED driver circuit means 106 is coupled to the
input of at least one LED shown generally at 164 to cause the LED
to turn on and off in accordance with the pulse train to generate
the digitally formatted optical wave 30. The digitally formatted
optical wave 30 contains the encoded dial tone frequency electrical
signal and is transmitted to the terminal unit 11. The optical wave
30 passes through the optical filter 36 and is sensed and detected
by a photo diode 166. The output 168 of the photo diode 166 is
coupled to an amplification and signal conditioning circuit means
shown generally within the function block 170 which removes analog
noise and "squares up" the leading and trailing edges of the
digital pulses in the pulse train. The digital signal is coupled
from the amplifier and signal conditioning circuit means to the
input 172 of a digital demodulator circuit means shown generally
within the function block 174 which decodes and transforms the
digital pulses into an analog electrical signal which at this stage
of the communication is the dial tone signal returned from the
public telephone network. The demodulated signal is coupled to the
input 176 of an amplifier shown generally within the function block
178 and whose output 180 is coupled to the input of an earphone 182
which transforms the electrical analog signal into an audio signal
which is heard by the user. Upon hearing the return of the dial
tone signal, a user now dials (taps the keys on the keypad) the
desired telephone number via the keypad and DTMF generator within
the function block 112. The analog electrical information in the
form of the DTMF signals is inputted to the amplifier 116 and is
processed through the terminal unit and received by the station
unit 18 in the same manner as the supervisory OFF-HOOK signal with
the exception that the signal at the digital demodulator circuit
means output 122 in the station unit is not sensed by the DTMF
detector and latching circuit means but, is coupled to the input of
a buffer amplifier circuit means 182 for amplification. The output
184 of the buffer amplifier circuit means 182 is coupled to the
input of the receive isolator 146 and to the public telephone
network through the phone line 136 via the two wire-to-four wire
hybrid converter 138 in the normal manner. Upon connection to the
called party, voice or other device, communication is established
and processed and returned to the terminal unit in a similar manner
as the dial tone signal is returned from the public telephone
network as described above. Upon establishing the connection to the
public telephone network, credit card, or other calling information
is provided as normal. The user now communicates in the normal
manner via a microphone 186 which transforms acoustic energy to an
electrical signal which is coupled to the amplifier 116 by the lead
188. The electrical analog signal corresponding to the audio signal
input, generally voice or data, to the microphone 186 is processed
and transmitted to the telephone line 136 in a similar manner as
the DTMF generated signals are processed.
The user may terminate a call by transmitting an ON-HOOK
supervisory signal to the station unit 18 by depressing a
predetermined key on the keypad 112 to generate a corresponding
DTMF signal. The DTMF signal is processed and transmitted to the
station unit in the same manner as the OFF-HOOK supervisory signal.
The ON-HOOK supervisory signal is received and sensed by the DTMF
detector and latching circuit means 124 and is outputted on lead
126 to the microprocessor 100. The instruction set in the
microprocessor 100 detects the presence of the ON-HOOK supervisory
signal and provides an output on the lead 128 causing the DTMF and
latching circuit means to release the relay 132 and drop the
connection to the telephone line 136. If the user does not wish to
proceed with any further calling to the public telephone network,
the ON/OFF enable switch shown within the function block 72 is
operated to its OFF position which disables the LED driver circuit
means to prevent the 56 kilohertz connection command signal whose
presence is required to maintain the optical communication link,
from being transmitted to the station unit. The absence of the 56
kilohertz connection command signal for a predetermined time
interval is detected by the microprocessor 100 which provides a
signal on the lead 128 to the DTMF detector and latching circuit
means 124 to remove the drive signal from lead 130 causing the
relay 132 to drop and disconnect the phone line from the pay
telephone and two wire-to-four wire hybrid converter 138 and to
return control of access to the tip and ring back to the pay
telephone instrument. The station unit circuitry continues to
operate for a predetermined time in the absence of the 56 kilohertz
connection command signal to accommodate momentary interruptions in
the optical communication link between the terminal unit and the
station unit as might be the case for example, if a person walks
between the terminal and station units momentarily breaking the
optical link. After the predetermined time interval, in the present
embodiment 3 seconds, the "target lock" drive signal on lead 108 is
removed from the LED 110 indicating to the user that the optical
communication link has been disconnected. The time interval is
adjustable through the instruction set stored in the
microprocessor.
Turning now to FIGS. 6 and 7, electronic circuit diagrams shown
partially in block diagram form are illustrated as one embodiment
of the present invention as it might be used to provide an optical
communication link with a pay telephone instrument connected to the
public telephone network. Referring to FIG. 6, a user initiates the
two way optical communication link by operating a switch 190 from
its OFF position 192 to its ON position 194. The transfer terminal
196 couples the gate 198 of an FET 200 to the output 202 of a
digital modulator circuit represented by the functional block
diagram 204. The digital modulator may be, as explained above,
implemented using pulse width modulation (PWM) or continuously
variable slope delta (CVSD) modulation techniques. One such CVSD
integrated circuit is available from Motorola Semiconductor and is
designated MC 3418. A 56 kilohertz clock signal is provided to the
digital modulator at its clock input 206 which is coupled to the
output 208 of a binary counter 210. The binary counter 210 receives
a 3.58 megahertz signal from a crystal oscillator generally
designated 212 coupled to the clock input 214,216 of the binary
counter 210. Upon operating the switch 190 to the ON position, the
FET 200 is biased to enable one or more LED's generally designated
218 having a respective cathode terminal 220 connected to the
source terminal of the FET 200. The LED will become conductive and
emit light when the FET is biased on to complete the circuit
between a voltage potential coupled to the anode 222 of the LED 218
and to ground potential 224 thereby forward biasing the LED. The
FET 200 is biased on and off at the 56 kilohertz rate causing the
LED 218 to provide a digitally formatted optical wave having an on
and off duty cycle of 50% and a frequency of 56 kilohertz.
A standard 4 row by 4 column keypad shown within the dash box 226
corresponds to the keypad on the handset and has its respective
columns 1, 2, 3, 4 coupled to the respective column input of a DTMF
generator designated by the function block 228 via leads 230, 232,
234, 236 corresponding to the respective columns 1-4. The
respective rows 1-4 are connected to the respective row input of
the DTMF generator 228 via leads 238, 40, 242, 244 corresponding to
rows 1-4 respectively. The crystal oscillator 212 is also coupled
to the clock input 246 of the DTMF generator. Upon operation of a
key in the keypad 226, one of the respective columns 1-4 is
connected to one of the respective rows 1-4 and the intersection
causes the DTMF generator 228 to produce a standard DTMF signal at
its output 248 and which signal corresponds to a standard pair of
tones well known to those skilled in the art.
The DTMF generator 228 also includes a shunting output 250 coupled
to the gate 252 of an FET 254. The FET 254 has a source terminal
256 coupled to one end 258 of a microphone 260 associated with the
handset and a sink terminal 262 coupled to ground potential 224.
During the generation of a multi-frequency signal, the FET 254 is
biased to its off state to create an open circuit between the lead
258 of the microphone 260 and the ground potential 224 thereby
preventing side tones from being coupled to the handset from the
output 248 through the series connection of the capacitor 262,
resistor 264, resistor 266, capacitor 268 and input lead 270
connected to the microphone 260.
The ON-HOOK, OFF-HOOK, and other supervisory signals are generated
utilizing the combination of the keys in the fourth column
intersecting with rows 1-4 of the keypad. In the illustrated
embodiment, an OFF-HOOK supervisory signal is generated by
depressing the key 272 associated with column 4 and row 2 to cause
the DTMF generator to produce the corresponding multi-frequency
tone signals at its output 248 which is coupled through the
capacitor 262 and resistor 264 to the input 274 of an amplifier
276. The output 278 of the amplifier 276 is coupled to the input
280 of the digital modulator 204 which processes and encodes the
analog signal present at its input 280 to digitally formatted
electrical pulse signals at its output 202. The digitally formatted
electrical pulse signals biases the FET 200 on and off to cause the
LED 218 to emit a series of optical pulses having a duration,
frequency and timing corresponding to the of the digital pulses
appearing at the output lead 202. Likewise, a voice or acoustic
signal inputted to the microphone 260 is transformed into an analog
electrical signal at the lead 270 and is coupled through the
capacitor 268 and resistor 266 to the input 274 of the amplifier
276. The output 278 of the amplifier 276 couples the analog signal
representative of the voice or other audio input to the microphone
260 to the input 280 of the digital modulator 204 where it is
processed and encoded to provide a series of digital pulses at the
output 202. The series of digital pulses at the output 202,
representative of the voice or other audio input signal, causes the
LED 218 to emit a corresponding series of light pulses which are
transmitted to the station unit.
An ON-HOOK supervisory signal is generated in a similar manner as
the OFF-HOOK supervisory signal and in the illustrated embodiment,
switch 282 is operated to connect column 4 and row 4 causing the
DTMF generator 228 to produce a standard multifrequency signal well
known to those skilled in the art. The ONHOOK multi-frequency
signal converted to a series of digitally formatted optical pulses
in the same manner as the OFF-HOOK supervisory signal.
The terminal unit also includes a photo diode 284 for receiving
digital optical pulses transmitted from the station unit, as
explained in further detail below, to electrical digital signals.
The LED 284 has its cathode 286 coupled to a voltage source and its
anode 288 coupled through a resistor 290 to ground potential 224.
The digital electrical pulse signals representative of the digital
optical pulses are coupled to the input 292 of a signal
conditioning amplifier 294. The amplifier 294 may be one or more
stages of amplification and signal conditioning to remove AC or
other analog noise from the converted optical signal. The output
296 of the last stage of amplification and signal conditioning is
coupled to the input 298 of an amplifier 300. The output 302 of the
amplifier 300 is coupled to one terminal 304 of a range switch
generally designated 306.
The range switch 306 has a second terminal 308 coupled to the input
298 of the amplifier 300. The amplifier 300 is switched in and out
of the circuit via the range switch 306 which has its transfer
contact 310 coupled to the transfer terminal 312 in series with the
output 302 of the amplifier 300. When the transfer contact 310
connects terminals 304 and 312, the distance between the terminal
unit and the station unit may be increased. In instances were the
distance between the terminal unit and the station unit is
relatively short, the range switch 306 is operated to connect the
switch terminal 308 to the transfer terminal 312 thereby by-passing
the amplifier 300.
The transfer terminal 312 of the range switch 306 is coupled
through a resistor 314 to the input 316 of an amplifier 318
configured as a pulse shaping circuit to "square off" the leading
and trailing edges of a digital pulse signal at its input. The
output 320 of the pulse shaping circuit is coupled to the input 322
of a digital demodulator circuit generally designated 324 which
decodes the encoded pulse train received at its input 322 and
converts the pulse train to an analog signal at its output 326. The
analog signal at the output 326 is coupled through a resistor 332
and shunt capacitor 334 functioning as a low pass filter to the
input 328 of an earphone generally designated 330. The earphone 330
converts the electrical signal to an audio signal which is heard by
the user.
A phaselock loop circuit represented generally by the function
block 336 has its input 338 coupled to the output 320 of the
amplifier 318 and the input 322 of the digital demodulator 324. The
input 338 also receives the series of digital pulses to derive a
synchronous clock signal at its output 340 based on the frequency
of the digital pulses present at its input 338. The clock output
340 is coupled to the clock input 342 of the digital demodulator
circuit 324 whereby the series of digital pulses present at the
input 322 are processed and decoded in accordance with the
frequency of the pulse train to replicate the analog signal at its
output 326 and which replicated signal has the amplitude and
frequency of the corresponding analog signal originating at the
station unit as explained below.
Turning to FIG. 7, a digitally formatted optical wave transmitted
by the terminal unit to the station unit is sensed and detected by
a photo diode generally designated 344 and which photo diode
converts the digital optical pulses received to corresponding
electrical digital pulse signals. The photo diode 344 has its
cathode 346 coupled to a voltage source and has its anode terminal
348 coupled to a ground reference potential 350 through resistor
352. The input circuitry to the station unit for receiving the
digitally formatted optical pulses is similar to the circuitry of
the terminal unit for receiving digitally formatted optical pulses.
The electrical pulses converted by the photo diode 344 are coupled
to an input 354 of an amplification and signal conditioning
amplifier circuit 356 to remove analog noise and other noise from
the received signal. Although the signal conditioning amplifier 356
is shown as one stage, it may be one or more stages. The output 358
of the amplifier 356 is coupled to the input 360 of an amplifier
362 which provides further amplification of a received signal. The
output 364 of the amplifier 362 is coupled to one terminal 366 of a
range switch generally designated 368 and substantially identical
to the range switch in the terminal unit. The range switch 368 has
a transfer terminal 370 which is connected to the output 364 of
amplifier 362 via the switch terminal 366 when the transfer contact
369 of the range switch is operated to the long range position to
permit an increase in distance between the terminal unit and the
station unit. The amplifier 362 is by-passed for short distances
between the station unit and terminal unit when the transfer
terminal 370 of the range switch 368 is connected to the terminal
372 by the transfer contact 369. The transfer terminal 370 is
coupled through a resistor 374 to the input 376 of a pulse shaping
circuit generally designated 378.
The pulse shaping circuit 378 sharpens up the leading and trailing
edges of a digital pulse signal present at the input 376. The
output 380 of the pulse shaping circuit 378 is coupled via lead 382
to an input 384 of a microprocessor designated generally by the
function block 386. The output 380 of the pulse shaping amplifier
circuit 378 is also connected to the input 388 of a digital
modulator circuit generally designated by the function block 390.
The digital modulator circuit 390 corresponds to the digital
transmission scheme being used, that is, in the preferred
embodiment pulse width modulation (PWM) or continuously variable
slope delta (CVSD) modulation. In the illustrated case, the digital
demodulator is of the CVSD type described above and includes a
phaselock loop circuit 392 having its input 394 coupled to the
output 380 of the pulse shaping circuit 378 to derive a clock
signal based on the frequency of the pulses, appearing at the input
394. The clock signal appearing at the output 396 of the phaselock
loop circuit is coupled to the clock input 398 of the digital
demodulator circuit 390. The output 400 of the digital demodulator
circuit 390 is coupled through a resistor 402 and capacitor 404
functioning as a low pass filter to the transmit input 406 of the
two wire-to-four wire hybrid converter shown within the dashed line
box 408. The analog output signal is also coupled to the input 410
of a dual tone multi-frequency (DTMF) receiver/decoder indicated
generally by the function block 412. A 3.58 megahertz crystal clock
designated generally 414 is coupled to the clock input 416,418 of
the DTMF receiver/decoder 412. The DTMF receiver/decoder 412
converts standard dual tone multi-frequency signals to
corresponding digital output signals on address output terminals
generally designated 420. Address leads generally designated 422
couple output terminals 420 to corresponding input address
terminals generally designated 424 of the microprocessor 386. Upon
receiving a connection command signal from the terminal unit when
the user operates the switch 190 to the ON position, the 56
kilohertz digitally formatted optical wave is received at the photo
diode 344 and is processed and conditioned similarly as a digitally
formatted optical wave received at the photo diode 284 in the
terminal unit. The digital pulses appearing at the output 380 of
the pulse shaping amplifier circuit 378, when the initiate
communication link command is activated, correspond to a 56
kilohertz pulse train which is coupled to the timer input capture
lead 384 of the microprocessor 386 which recognizes that the signal
present at the capture lead 384 is the frequency corresponding to
the connection command signal. The microprocessor 386 responds and
provides a target lock signal at its output 426 which is coupled to
the gate terminal 428 of an FET 430. The source terminal 432 of the
FET is coupled to the cathode 434 of an LED 436 which has its anode
438 coupled to a voltage source. The FET 430 has its sink terminal
440 coupled to ground reference potential 350. The capture signal
at the output 426 biases the FET 430 to its conductive state which
causes the LED to become forward biased and emit light indicating
to the user that the optical link connection is established and
that the terminal unit and station unit are in proper
alignment.
The microprocessor 386 also provides an enable/disable signal at
its output 442 which is coupled to the gate terminal 444 of an FET
446 and the LED 448 is disabled by shunting the gate terminal 450
of the FET 452 to ground reference potential 350 through the
conductive path formed by the source and the sink terminals of the
FET 446. When the FET 446 is made nonconductive by the presence of
an enable signal at the gate 444 from the microprocessor 386, the
FET 452 is now conditioned to be turned on and off upon application
of the proper polarity signal at its gate terminal 450. The LED 448
has its anode 454 coupled to a voltage source and has its cathode
456 coupled through a resistor 458 to the source terminal 460 of
the FET 452. The sink terminal of the FET is coupled to ground
reference potential 350. The LED 448 will turn on and off to
produce the digitally formatted optical signal in accordance with
the pulse signals applied to the gate terminal 450 biasing the FET
452 on and off.
The DTMF receiver/decoder 412 also produces a clock signal at its
output 462 which is coupled to the clock input terminal 464 of the
microprocessor 386 and to the input 466 of a binary counter
generally designated by the function block 468. The output 470 of
the binary counter 468 is coupled to the input 472 of a digital
modulator circuit designated generally by the function block 474.
The output clock signal at the lead 470 is a 56 kilohertz 50%
duty-cycle pulse train. The signal at the output 476 of the digital
demodulator circuit 474 is coupled to the gate terminal 450 of the
FET 452 through the resistor 478. The signal at the output 476 is a
56 kilohertz pulse train which causes the LED 448 to emit a series
of optical pulses at the 56kilohertz rate. The user may now elect
to transmit an OFF-HOOK supervisory signal as described above and
which signal is transmitted in a digitally formatted optical signal
and received by the photo diode 344 and processed as indicated
above. The analog DTMF signal transmitted from the terminal unit is
replicated at the digital demodulator output 400 and is coupled to
the DTMF receiver/decoder 412 through the resistor 402 and
capacitor 480. The DTMF receiver/decoder 412 provides a decoded
signal at its address output terminals 420 which are coupled via
the address leads 422 to the microprocessor address lead inputs
424. The microprocessor 386 detects the OFF-HOOK supervisory signal
and produces a signal at its output 482 which is coupled to a gate
terminal 484 of FET 486. The source terminal 488 of the FET 486 is
coupled to one end 490 of a relay 492. The sink terminal 494 is
coupled to the ground reference potential 350 and when the FET 480
is made conductive, the relay 492 operates causing its respective
transfer terminals 496,498 to operate to connect the tip and ring
of the telephone line respectively to the two wire input of the two
wire-to-four wire hybrid circuit 408.
Dial tone is now received from the central office in the normal
manner and is coupled through the two wire-to-four wire hybrid
circuit 408 to the receive lead 500. The receive lead 500 is
coupled to the input 502 of an analog switch 504 which provides an
electrical path from its input 502 to its output 506 when a proper
polarity control signal is present at its control input 508. The
control input 508 is coupled to a control output 510 of the
microprocessor 386 which generates the control signal when the
OFF-HOOK supervisory signal is received and recognized. The dial
tone signal is coupled through the analog switch 504, through
capacitor 512 and resistor 514 to the input 516 of an amplifier
518. The output 520 of the amplifier 518 is coupled to the input
522 of the digital modulator circuit 474. The dial tone signal
appearing at the input 522 to the digital modulator 474 is
processed and encoded as digital pulses and appear at the output
476 of the digital modulator. The digital pulses are converted and
transmitted as a digitally formatted optical signal by the LED 448
as described above. Similarly, analog signals at the terminal unit
are processed and converted to a digitally formatted optical signal
which is transmitted to the station unit, processed and converted
to an analog signal, and sent to the tip and ring of the telephone
line connected to the public telephone network via the two
wire-to-four wire hybrid circuit. Likewise, analog signals received
from the tip and ring of the telephone line network are processed
and converted in the station unit and transmitted as a digitally
formatted optical signal to the terminal unit where they are
processed and decoded to replicate the incoming analog signal.
Upon completion, a user may terminate the call by generating an
ON-HOOK supervisory signal from the terminal unit as described
above and which supervisory signal is recognized by the
microprocessor 386 in a similar manner as is the OFF-HOOK
supervisory signal to cause the FET 486 to become non-conductive
thereby releasing the relay 492 and opening the tip and ring
connection to the two wire-to-four wire hybrid circuit. If a new
call is to be made, the user now transmits a new OFF-HOOK
supervisory signal to repeat the call process as in any normal
telephone communication calling sequence. If the user wishes
instead to terminate the call and disconnect the communication
link, the switch 190 is operated to its OFF position which inhibits
the transmission of the 56 kilohertz optical pulse signal to the
station unit. The microprocessor 386 maintains the "target lock"
for a predetermined time after the 56 kilohertz signal is
interrupted or disconnected after which time a disable signal is
generated by the microprocessor at the output 442 to cause the FET
446 to become conductive thereby inhibiting the LED 448.
The present invention also features the capability to provide voice
messages or instructions during the calling process. For example,
at the time the microprocessor 386 provides a target capture signal
at its output 426, it also provides a command signal at its output
524 which is coupled to the input 526 of a voice synthesis message
circuit designated generally by the function block 528 to select a
message to be transmitted to the user. The output 530 of the voice
synthesis message circuit 528 is coupled to the input 532 of an
analog switch 534 which upon receipt of a command signal at its
control input 538 operates to connect the input 532 to its output
536. The voice synthesis message output 530 is coupled to the input
516 of the amplifier 518 through the analog switch 534, the
capacitor 542 and resistor 544. A selected voice synthesis message
is processed in the same manner as any analog electrical signal
inputted to the amplifier 518 and is transmitted to the terminal
unit via a digitally formatted optical signal to provide
instructions for operating the terminal, placing a call, prompting
instructions, for example, instructions to a user to operate the
OFF-HOOK key on the keypad to get dial tone. Similar messages,
preprogrammed advertisements, and so forth that are desired to be
conveyed to a user may be stored in the voice synthesis message
circuit, each of which may be address selectable by the
microprocessor output 524 connected to the input 526 to the voice
synthesis message circuit 528.
Apparatus for providing a two-way digitally formatted optical
communications link has been described above in several preferred
embodiments. It will be understood by those skilled in the art that
although pulse width modulation and continuously variable slope
delta modulation digital transmission protocols are described, the
present invention is also operable with any digital baseband
modulation scheme. Therefore, the present invention is disclosed by
way of illustration rather than limitation.
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